What did Wendi Deng first see in the billionaire Rupert Murdoch? It's the oldest joke in the book and one that has long been directed at this relationship – by everyone from supposedly hostile Murdoch family members, who have expressed their disdain since the media mogul tied the knot with her on his yacht, Morning Glory, in 1999, to the media and the world at large.

But if octogenarian Murdoch's fumbling – and even at times confused – performance at the House of Commons on Tuesday was surprising, it paled into insignificance, in terms of theatrics at least, of his third wife. The impeccably groomed and until that point inscrutable Deng leapt to his defence, unceremoniously slapping the improbably named "pie man", Jonnie Marbles, and thereby deflecting his assault long before anyone as effective as a security guard, say, had the good sense to intervene.

Deng, in a reassuringly expensive rose-pink jacket, cornflower blue shirt and black skirt, and with long, dark hair, sat behind her husband on doubtless the most difficult day of his long career. Her dignity and self-discipline were palpable – particularly as compared with the ruffled and defensive behaviour of the two other women in his life: daughter Elisabeth and erstwhile chief executive Rebekah Brooks.

Wendi gently discouraged Mr Murdoch from banging the desk in front of him – image control doesn't come much more finely tuned than this – smiled at him, and rubbed his back when the going got particularly tough. It looked like genuine affection – and it probably was.

Those far less likely to sympathise with Murdoch's predicament have since admitted to feeling compassion for him, after all – although admittedly of the kind more usually directed towards a marginally dotty, errant old uncle as opposed to an equal or spouse.

Whatever, every detail of her behaviour and physical appearance was immaculately well-mannered – note the Chanel Particulière nail polish, a well-chosen and suitably understated touch when, as it soon turned out, she might be more suited to Vamp.

It was all just as one might expect from the wife of one of the world's most powerful men. Her reaction to a threat to his personal safety was clearly instinctive, however, and in no way planned. And what instincts. "At last the News of the World enquiry has exposed News Corps deepest darkest secret," wrote the journalist Joe Hildebrand on Twitter. "Wendi Deng is a Power Ranger."

So a new media heroine (or should that be superhero?) is born, and one who is a more formidable prospect than either Kate Middleton or Victoria Beckham, to name perhaps the two most conspicuous examples beloved by this country's press – not least for their predominantly passive behaviour and for being shrinking violets by comparison with Mrs Murdoch.

Although increasingly well known in the US, Deng's profile here has been relatively low until now – her husband Rupert appeared to prefer it that way, in the early days of their marriage especially. Interviews with her are still unheard of. When The Wall Street Journal (not then Murdoch-owned) ran a lead feature in the year 2000 on his new wife's quiet but significant influence, he was reportedly not amused, and she subsequently refused to speak to the journalists who penned it. "As the wife of the chairman and a private citizen, Wendi is entitled to her privacy," the then News Corp spokesperson, Gary Ginsberg, said, words that are nothing if not ironic as it turns out.

In 1999, Murdoch told Vanity Fair magazine that his relationship with his wife ruled out her working for News Corp at that point. Instead, she was "busy working on decorating the new apartment" in Manhattan, social X-ray style. Later, it is thought that he pulled a profile of her written by a contributor to Fortune magazine and destined for an Australian newspaper chain he partly owned at the time.

The truth will invariably out, however, as Mr Murdoch has learnt elsewhere to his immense cost. More recently, his wife's reputation as a behind-the-scenes trouser-wearer par excellence, both personally and professionally, precedes her. In Michael Wolff's biography of Murdoch, he writes of Deng: "Let's recast this story as a triumphal, even uplifting tale of pluck and achievement. She's not [William Makepeace Thackeray's cynical social-climbing heroine] Becky Sharp, she's Pip in Great Expectations." Certainly, the lady has done spectacularly well for herself. In her home country she is, by all accounts, something of a role model to thousands of young Chinese women, many of whom see her rise to wealth and Western supremacy as nothing short of inspirational as, on at least some levels, indeed they might.

She was born Deng Wen Ge – one of three children and the daughter of a factory manager – and grew up in eastern China, simplifying her name to Wendi in her mid-teens.

While studying medicine, aged 16, she met the Californian couple, Jake and Joyce Cherry, who had been posted to the region. They would turn out to be her ticket to the West. Proving herself a tough cookie from the start, Deng persuaded the Cherrys to sponsor her for a student visa to the US.

Mrs Cherry's help and affection was rewarded by her young protégé promptly running off with her husband – 30 years her senior. They married but lived together for no more than a few months. It wasn't long before Deng was embroiled in an affair with David Wolf, a man of her own age, and a little less than three years later, she and Jake Cherry divorced. Mr Cherry told The Wall Street Journal: "She told me I was a father concept to her, but it would never be anything else. I loved that girl."

With an MBA from Yale University and a degree in economics, Deng was then employed by Star TV, News Corp's Asian satellite-television operation in Hong Kong, as an intern in 1996. She met Murdoch in 1998 when she was assigned the job of his interpreter in Shanghai and Beijing – rumours of a blossoming relationship of a more intimate nature between them began circulating a matter of months after that.

It is unsurprising that Deng, 42, has attracted the requisite jibes reserved for much younger wives. When Anna Nicole Smith died, Private Eye published a picture of her as a dominatrix captioned with the words: "Anna Nicole Deng: the scheming temptress who stole her way into the heart of a foolish old man – and stole all his money as well".

On the other hand – and equally the stuff of cliché – Murdoch has been accused of being attracted to her more for her abilities to ease his entry into China than anything as straightforward as, for example, youth or beauty. She is fluent in Mandarin in an age where expansion into that continent is the economic Holy Grail – and as well as acting as a quasi-ambassador for News Corp there, she has been chief strategist for MySpace China.

She is also co-founder and co-CEO of the film company Big Feet productions – Snow Flower and the Secret Fan happens to be its current project, and will have a giant publicity boost after this week. In short, she's anything but a trophy wife.

Privately, Deng has proved a softening influence on Murdoch who, thanks to his wife, is prepared to go to work dressed in chinos and black turtleneck where previously only a suit or tie would do. He's also sporting more modish heavy-framed glasses these days. The aforementioned Manhattan home, meanwhile, was reportedly designed according to the diktats of feng shui, which it is difficult to imagine Murdoch actively embracing without his wife's input.

Wendi Deng is now the mother of Grace and Chloe, two potential heiresses of Murdoch's. Although his children from former marriages – Prudence, Lachlan, Elisabeth and James – and his second wife, Anna, fought his attempts to give his youngest progeny a say in the running of his empire, the young children will benefit from his fortune nonetheless. In 2007, both Grace and Chloe received $100m (£62m) in stock from their father.

So what next for Wendi Deng? If past form is anything to go by, she will continue to stand by her man while the rest of the world decries him and, for that, she may prove to be his finest asset.

Straight after the pie-throwing incident, social-media sites were lit up with praise for Deng – some ironic, but much of it genuine admiration. "Wendi heroic protector of fading old genius," tweeted Channel 4 News' Jon Snow not long after her by-now legendary intervention.

So during a scandal that continues to erupt around the name Murdoch, this relatively unknown character has, in a matter of seconds, lent a tender aspect to the story. Even the most adept of publicists (or damage-limitation experts) would have been considered foolhardy ever even to have dreamt of that.